Casing cutting system



Jul 25. 1967 Filed April 15, 1965 wann- R. P. THOMA 5 CASING CUT'I ING SYSTEM OCEAN FLOOR 2 Sheets-Sheet l ROY F. THOMAS INVENTOR ATTORNEY July 25, 1967 R P. THOMAS CASING CUTTING SYSTEM Filed April 15, 1965 FIG.3

2 Sheets-Sheet 2 ROY F? THOMAS INVENTOR.

ATTORNEY United States Patent O ABSTRACT OF THE DISCLOSURE This relates to a method and device for use in cutting well casing which has been set in marine locations. It includes setting a well plug in the casing at a location immediately below the point at which the casing is to be cut. A special rotating base sub is connected to the lower end of a conventional cutter. The base sub has upper and lower sections which are rotatably attached. The lower section of the rotating base sub engages the plug in a non-rotating relationship and the cutter is then rotated by rotation of a drill string on a drilling vessel.

This system relates to the cutting of casing set in well bores. It relates especially to a method and device for use in cutting casing which has been set in marine locations.

When drilling wells for the production of oil and gas, it is necessary to place one or more strings of tubular material, commonly called casing, in such wells. The casing is normally made of steel and serves several purposes. For example, it prevents the walls of the well from caving, it excludes water from oil producing formations, and it prevents the waste of oil and gas from seeping into porous strata overlying the productive horizon. When wells are drilled in marine locations there are usually several strings of concentric casing set and cemented in place. In addition to serving the purposes listed above, these casings also serve as support for underwater wellhead equipment.

Unfortunately, many exploratory wells are dry holes, i.e., they are non-productive of oil or gas and must be abandoned. When an offshore well is to be plugged and abandoned, one requirement is the removal of all obstacles such as the casing strings from the ocean floor to some distance below the mud line. This also provides for the salvage of a considerable amount of casing and normally expensive subsea wellhead equipment. This removal of obstacles necessitates the cutting of the casing strings. Several methods are available for cutting or parting casings. One such method is the use of explosive charges for parting the casing. Another method is cutting which includes jetting an abrasive fluid against the casing until it is parted or by use of an expanding blade mechanical cutter. In these two cutting methods the jets or blades are rotated by the drill pipe which supports the jet cutter or the mechanical cutter. In order for these two cutting methods to concentrate the cutting action along a single horizontal plane, the jets or blades must be held in a constant horizontal plane.

These systems of parting or cutting the casing all have rather serious restrictions or objections. The explosive charge, while being quite effective, has disadvantages in its inherent hazards and in the possible damage which it may do to the wellhead equipment. To prevent this dam age, sometimes the wellhead equipment is removed by divers before the explosive charges are detonated. This is a costly operation. It is nearly impossible to use cutting methods using jets or blades inasmuch as they must be held in a constant horizontal plane which cannot be done by the drill string alone as is done on land operations. This is because of the heaving, or up and down motion, of the floating vessel. Due to the previous inability to maintain the mechanical cutters in a single horizontal plane, the explosive charge method has been predominantly used for cutting of casing when a marine well is to be abandoned as this method is unaffected by the heave of the drilling vessel. Due to the disadvantages of using explosive charges it is clear that there is a need for improvements whereby non-explosive type cutters can be used for cutting casings in offshore wells drilled from floating vessels and which are to be abandoned. Such a system is disclosed herein.

A method and apparatus are disclosed by this invention which makes it possible to maintain an expanding type blade mechanical cutter in a single horizontal plane at the desired depth for cutting casing strings in a marine well drill from a floating vessel. This system broadly includes the setting of a permanent plug within the casing immediately below the depth at which it is to be cut. This plug serves as a base or reference point from which the cut of the casing is made. A rotating-base sub means is provided and is attached to the lower end of a mechanical cutter, for example, which is suspended in the casing by a drill string from a floating vessel. In operation the drill string is lowered until the rotating-base sub engages the upper end of the casing plug. The rotating-base sub provides for a rotational but fixed longitudinal relationship between the cutter and the plug. The reaction thrust from the cutter is transmitted through the sub to the plug. The plug thus provides a fixed point upon which the cutter turns without being moved vertically by heaving of the floating vessel.

A better understanding of the invention and other objects thereof will become apparent from the following description taken in conjunction with the drawings in which:

FIGURE 1 illustrates a typical setting of casing in a marine location and includes a bridge plug and cutting equipment used in this invention.

FIGURE 2 illustrates a sectional view taken along the line 22 of FIGURE 1.

FIGURE 3 illustrates a rotating-base sub.

FIGURE 4 illustrates a section taken along the line 4-4 of FIGURE 3.

Shown in FIGURE 1 is the ocean floor 10 in which a well has been drilled and a plurality of strings of casing has been set. This includes an outer string 12, an intermediate string 14, and an inner string 16 and in which cement has been placed in the annular spaces 18 and 20. Typically, casings 12, 1.4, and 16 can be 30", 16", and 10% in diameter, for example. Intermediate string 14 is frequently provided with stabilizer fins 22.

Immediately below the point at which it is desired to cut the casing there is set a plug 24. This can be, for example, a type DC casing bridge plug, commercially available from Halliburton Company, Duncan, Okla. The top mandrel 26 is preferably modified to include key slots 28 as shown more clearly in FIGURE 2.

Above bridge plug 24 there is illustrated a drill string 30 from which is suspended a slip joint 32, a mechanical cutter 34, and a rotating-base sub 36. Drill string 30 is supported from a floating vessel by known means (not shown). Slip joint 3-2 can be a Shaffer slip joint, commercially available from Shaffer Tool Works, Brea, Calif. The preferred location of the slip joint is just above the casing cutter. One form of slip joint is essentially an expansion joint in the drill string to compensate for vertical motion of the drilling vessel. A lower section of drill pipe 38 connects the slip joint 32 to cutter 34. Cutter 34 is commercially available and can be, for example, an A-l Big Inch casing cutter and mill, commercially available and manufactured by the A-1 Bit and Tool 3 Company, Oklahoma City, Okla. Cutter 34 has expandable cutters 49 which are extended after the cutter assembly has been lowered to the desired point.

A rotating-base sub 36 is connected through a double pin joint 42 to the lower end of cutter 34. Other type connections between rotating-base sub 36 and the cutter 34 can be made.

Attention is next directed toward FIGURE 3 which shows the details of a preferred embodiment of the rotating-base sub. This includes a lower non-rotating base or section or barrel assembly 44 and an upper rotating section 46 which may also be called a thrust mandrel. The lower barrel assembly 44 has internal bore 48 adapted to receive thrust mandrel 46. Thrust mandrel 46 is rotatably connected to the lower barrel assembly 44. Mandrel 46 has an external groove 50 which mates with an internal groove 52 in the bore 48 of the barrel assembly 44. Threaded plug 54 is provided in the wall of barrel assembly 44 for inserting retaining bearings 56 into the annular groove formed by groove 50 and 52 to form a retaining bearing. Packing means 58 which is held in place by packing nut means 60 provides a fluid seal between the exterior of thrust mandrel 46 and bore 48. This also protects the bearings from outside mud. Thrust bearings 62 are provided between the lower portion or annular shoulder 67 of thrust mandrel 46 and annular shoulder 45 of bore 48 of the lower barrel assembly 44. A reduced coaxial extension 64 of thrust mandrel 46 extends into a reduced bore 66 of the barrel assembly. Packing 68 is provided between such extension 64 and such reduced bore 66. A longitudinal passageway is provided through the thrust mandrel and barrel assemblies. This includes a bore 70 in thrust mandrel 46 and bore 72 in barrel assembly 44.

Connected to the lower end of barrel assembly 44 is a driver sub 74. When assembled, bore 72 extends into or communicates with bore 76 of driver sub 74. Port means 78 provides communication between bore 76 and the exterior of the tool. This permits circulation of drilling fluid during cutting operations.

The lower end of driver sub 74 is arranged or constructed to complement mandrel 26 and key slots 28 of plug 24. This includes internal keys-80 and bore 82. Bore 82 is slightly larger than the external diameter of mandrel 26. The lower end of driver sub 74 is tapered inwardly and upwardly; preferably angle a is about 45 to aid in facilitating engagement with mandrel 26. When the device is lowered into engagement with plug 24, the lower section of the rotating-base sub is held against rotation and the upper section or thrust mandrel 46 is free to rotate with cutter 34.

Having described the structural features of this invention, attention will now be directed briefly to its operation. The first thing to be done is to locate properly the casing bridge plug 24. The lower point on mandrel extension 26 of plug 24 is set at distance A below the depth at which it is desired to cut the casing. The distance A is shown in FIGURE 1 and is the vertical distance from cutters 40 when extended to the lower end of driver sub 74. Drill string 30, together with slip joint 32, cutter 34, and rotating-base sub 36 is lowered inside the inner casing 16 and manipulated until driver sub 74 is positioned about mandrel 28 and keys 86 has slipped into keyways 28.

At this time drilling fluid is circulated downwardly through drill string 30. Cutters 40 are extended either mechanically or by hydraulic pressure, depending on the particular type cutter selected, and the drill string rotated to cut the pipe at the desired location. When using the type cutter 34 referred to above, hydraulic fluid, i.e., the circulating drilling fluid, tends to force the cutters 40 upwardly into the Walls of the casing. The reaction thrust is transmitted downwardly through thrust mandrel 46, thrust bearings 62, lower barrel assembly 46, driver sub 74, to the set bridge plug 24. As the drill string is rotated,

drilling fluid is circulated downwardly through the drill string, out ports 78, and up the annulus between the drill string 30 and the inner casing 16. This also clears away cuttings made by cutters 40. Any heaving of the drilling vessel within reasonable limits is absorbed by slip joint or travel joint 32. Slip joint 32 can compensate for up to five or ten feet or more heave of the vessel without disturbing the vertical position of cutter 34. It is thus seen that by the use of my invention the casing can be cut at the exact depth desired by using a mechanical or jet type cutter and that such depth is not influenced or varied by the heaving of the vessel.

The apparatus and technique of my invention offer several advantages not obtainable with the normally used explosive cut-off methods. For example, assume that a well is drilled from a floating vessel and upon evaluation, it is decided that the well should be abandoned. The well is plugged in the proper manner and at that time by using my system, a cut off can be made with the drilling vessel and the subsea risers and other equipment still in place. (When using explosives the subsea risers, wellhead, etc., are removed before the explosive charge is detonated.) After the casing strings have been cut in accordance with my invention, the entire assembly above the cut can be retrieved together in an undamaged condition. This saves considerable time and permits subsea equipment, such as wellhead body, casing hangers and pack offs, landing joints, starting base, and guide lines to be retrieved in much better condition than is possible with an explosive type out off. There is also considerably less hazard involved in making a mechanical out than in handling explosive materials on board the floating drilling vessel. Further, service of divers to assist in the recovery is not required with this new technique since all recoverable items are retrieved together.

It is to be understood that the apparatus and system contained in the above description are merely representative and illustrative and are not to be construed as limiting the invention as many modifications may be made therefrom without departing from the spirit or scope of the invention.

I claim:

1. An apparatus for use with a cutter for cutting a casing lining a well bore comprising:

a plug having an upwardly extending mandrel having keyways, said plug set in said casing;

a base sub having an upper section and a lower section;

said upper section including means for attaching said upper section rigidly to said critter;

said lower section including a driver sub means adapted to fit over said mandrel of said plug, including keys for fitting into the keyways of said mandrel;

means connecting said upper section and said lower section in a rotatable and fixed longitudinal relationship.

2. An apparatus for use with a cutting tool for cutting a casing in which a plug having an upwardly extending mandrel with keyways has been set just below a depth at which it is desired to cut the casing which comprises:

a hollow thrust mandrel having a first portion of one diameter and an extension of reduced diameter from that of the first portion, a circumferential groove intermediate the ends of said first portion, and an annular shoulder formed by the lower end of said first portion adjacent said extension;

a barrel member having a first bore opening at one end of a diameter slightly larger than the. diameter of said first portion of said thrust mandrel and having a bore extension of reduced diameter which is slightly larger than the diameter of the extension of said thrust mandrel such that said barrel member can receive said thrust mandrel, said barrel member having an annular groove on the interior of said first bore for mating with the external groove of said thrust mandrel to form a bearing retaining groove,

the first bore forming an annular shoulder within said barre-l member at the beginning of said bore extension;

retaining bearings within said bearing retaining groove;

4. An apparatus for use with a cutter for cutting a casing linear in a well bore and in which a plug has been set which comprises:

an upper section including means for attaching said packing means between the interior of said barrel mem- 5 upper section rigidly to said cutter;

ber and the exterior of said thrust mandrel and posia lower section including means for engaging said plug; tioned above said annular groove; means connecting said upper section and said lower seea thrust bearing between said annular shoulder of said tion in a rotatable and fixed axial relationship;

thrust mandrel and said annular shoulder of said said upper section and said lower section having a barrel member; 10 longitudinal conduit means t'herethrough;

a driver sub connectable to the lower end of said barrel member, including means establishing fluid communication betweenthe interior of said bore extension and the exterior of said driver sub;

the lower end of said driver sub containing an open said lower section having port means establishing a fluid communication between said longitudinal conduit means and the exterior thereto.

5. An apparatus as defined in claim 4 in which said lower section has a receiving bore opening at its lower bore having internal keys for mating with the keyways of said mandrel of said plug, the lower end of said driver sub sloping inwardly and upwardly. 3. An apparatus for cutting a casing in a well from a floating vessel in a marine location which comprises:

end and an internal key thereon, the lower end of said lower section being tapered inwardly and upwardly into the said receiving bore.

References Cited a plug set just below a depth in the Well at which it is UNITED STATES PATENTS desired to cut the casing; a drill string including a slip joint; 5 23 n a casing cuttenattached to said drill string at a point 2134796 11/1938 ozmun 8 below 831d shP 101m? 2,270,923 1/1942 Browne 285--276 a rotating base sub connected to the lower end of said 2 501 761 3/1950 D,Arc 166 7 cutter, said rotating base sub including an upper sec- 3012608 12/1961 z 1 tion connected to the lower end of said cutter and u a lower section engaging said plug in a non-rotating relationship, and means connecting said upper section and said lower section in a rotatable and fixed axial relationship.

CHARLES E. OCONNELL, Primary Examiner.

JAMES A. LEPPINK, Examiner. 

3. AN APPARATUS FOR CUTTING A CASING IN A WELL FROM A FLOATING VESSEL IN A MARINE LOCATION WHICH COMPRISES: A PLUG SET JUST BELOW A DEPTH IN THE WELL AT WHICH IT IS DESIRED TO CUT THE CASING; A DRILL STRING INCLUDING A SLIP JOINT; A CASING CUTTER ATTACHED TO SAID DRILL STRING AT A POINT BELOW SAID SLIP JOINT; 